Trying to get svn2git working on Windows

Obviously, rubygems.rb is missing. Install it as documented here:
https://rubygems.org/pages/download

Then, install svn2git as instructed here:
https://github.com/nirvdrum/svn2git

After that, everything shall be fine.

I'd suggest you to try SubGit tool. It does translate Subversion tags as tags and works well on Windows (requires Java 5 or newer). SubGit is ready to use. You may get latest build at download page and read documentation on the web site.

Originally in 2012 early SubGit versions required local access to Subversion repository (over file system) but later on (by 2015) on network access to subversion was added.

Disclaimer: I'm SubGit developer.